The present invention relates to the field of needled textile structures and it relates more particularly to a needling machine of the circular type.
Circular type needling machines are now well known, as shown for example by patent applications FR 2 626 294 or EP 0 849 389. In those conventional machines, the textile structure is needled by relative angular rotation between a horizontal platen supporting the structure and a needling head performing vertical reciprocating motion. In general, because of the reciprocating motion of the head, it is the support platen which rotates and it is the needling head which does not rotate. Furthermore, in order to keep the preform on the platen during rotation and in order to guarantee that it is properly held down, the platen is covered in a material that allows needling to take place, such as a succession of polypropylene fiber felts interconnected by adhesive or stitching (see for example application EP 0 232 059) or a set of brush mats (EP 0 849 389).
That circular machine configuration with a brush (or felt) platen unfortunately presents numerous drawbacks. Firstly the difficulty in securing the first layers of the preform generally makes it necessary to perform over-needling on them, which not only modifies needling density in the preform in said first layers, but also raises a problem when the preform is to be removed, since it must then be torn away from the brush or taken away together with the felt. Further, when the fibers for needling are of a brittle type such as carbon fibers, a particularly large amount of pollution is produced in the brush, which must be cleaned frequently in order to avoid the machine becoming dirtied to an extent that is harmful to making preforms. Finally, the flexibility provided by the presence of a brush or a belt, whereby the brush or felt is compressed to an increasing extent with increasing thickness of the preform, means that it is not possible to know the exact position of the top surface of the preform, and thus that it is not possible to have full control over needle penetration.
The present invention thus proposes mitigating these drawbacks with a circular needling machine of a novel type enabling annular preforms to be made having a structure that is particularly homogeneous. An object of the invention is also to propose a machine that is well adapted to needling textile structures made of brittle fibers, and in particular carbon fibers.
These objects are achieved by a circular needling machine for needling an annular preform made from a fiber fabric of material to be needled, the machine comprising a vertically movable needling table serving as a horizontal support for said annular preform, and a needling head comprising a determined number of barbed needles overlying a needling zone of said needling table and driven with vertical reciprocating motion, wherein said annular preform is placed directly on said needling table and is driven in rotation on said needling table by drive means, said needling table remaining rotationally stationary during said rotation.
This revolutionary structure for a circular needling machine using a platen or table that is xe2x80x9csmoothxe2x80x9d makes it possible to provide annular preforms presenting needling density that is uniform throughout the thickness of the preform and in which the various layers are of constant thickness.
In a preferred embodiment, the drive means for the annular preform comprise a set of conical friction rollers kept continuously in contact with said annular preform. Preferably, said set of conical friction rollers comprises three rollers advantageously disposed at 120xc2x0 and each actuated by an independent motor and gear box unit.
The needling table comprises a plurality of localized perforations for receiving said barbed needles during the first needling passes and it is preferably coated in an anti-friction material.
In an advantageous embodiment that is more particularly suitable for making preforms out of brittle fibers, the needling table forms the top wall of a suction box for removing fiber residues.
The needling machine of the invention can further comprise at least one conical backing roller placed in an opening in said needling table and designed to cooperate with at least one of said conical drive rollers. Preferably, said conical backing roller is mounted idle.
The present invention also provides the needling method implemented in the above-specified circular needling machine.